Transparency disappearing act
There were objects on meshes added after the transparent object was added. These objects failed to appear through the transparent object.
The transparent object was on its own mesh.
Objects, added before the transparent object was added, appeared through it.

Moving the later added objects higher, in the Scene outliner, remedied the problem.
Objects were moved by creating new meshes and making them the parent of the objects added after the transparent object.
There's probably a better way to do this, but I'm just grateful to have found a solution.